1. Technical Field
The present invention relates to a pulse generation circuit for generating pulses suitable for Ultra Wide Band (UWB) communication, and a UWB communication device.
2. Related Art
The UWB communication is a communication method for performing high speed large capacity data communication using a very wide frequency band. As the communication method using wide-band signals, there are cited a spread spectrum system and orthogonal frequency division multiplexing (OFDM) in the related art. However, UWB is a further wide-band communication method using pulses with very short period of time, and is also called impulse radio (IR) communication. In the IR systems, modulation and demodulation can be performed only by time-base operations in contrast to the modulation in the related art, and simplification of the circuit and reduction of power consumption are considered to be expected (see the specifications of U.S. Pat. No. 6,421,389, US-2003/0108133-A1, and US-2001/0033576).
Hereinafter, pulse waveforms used for the IR systems will briefly be explained with reference to the drawings.
The pulse train with a pulse width PD and a period TP shown in FIG. 17A, as well known, has a frequency spectrum, which is a sinc function with an envelope having the first zero point at the frequency of BW=1/PD as shown in FIG. 17B.
The pulse as shown in FIG. 17B is hard to use because the pulse has the spectrum extending from direct-current to BW, and the pulse having the center frequency f0 of the spectrum in a high frequency band as shown in FIG. 17D has the preference. This pulse waveform is obtained by cutting rectangular waves with the frequency f0=1/(2PW) from the pulse shown in FIG. 17A to shift the frequency spectrum towards a higher frequency. It should be noted that this waveform includes the direct-current (DC) component as illustrated with the dashed line 1301 in FIG. 17C, and therefore, does not have the ideal spectrum as shown in FIG. 17D, to be exact.
The waveform having such an ideal spectrum is shown in FIG. 17E. This waveform is obtained by multiplying the pulses shown in FIG. 17A by the sinusoidal wave with the carrier frequency f0. Further, FIG. 17F shows a waveform obtained by multiplying the pulses shown in FIG. 17A by a rectangular wave with the carrier frequency f0, which can easily be generated by a digital circuit. Since the pulse width is so narrow that such a square waveform is not formed even by the digital circuit, the waveform shown in FIG. 17E can be obtained. Although there are designed various other pulse waveforms ideal for the UWB communication different from the waveform shown here, since the generation method is simple, it is used frequently.